Tropical forest dynamics in logged, restored and conserved forests in SE Asia

Over half of all tropical forests are degraded by human impacts and activities such as logging, leaving them threatened with conversion to other types of land use (particularly agriculture) and risking substantial losses to biodiversity, carbon and a host of important ecosystem services that forests provide.  Stemming from research that began with the EU-funded INDFORSUS project (1995-1998) Prof. Mark Cutler has continued examining the impacts of both anthropogenic disturbance and climate change on forests in SE Asia through a series of projects funded by the Carnegie Trust for the Universities of Scotland and the UK Natural Environment Research Council (NERC).

Recent research has focussed on two particular aspects of forest dynamics: (i) the effectiveness of forest restoration measures on accumulated carbon density (ACD) in logged forests, and (ii) the impact of El Niño-driven drought on leaf traits and forest functioning in areas of intact primary forest.  From airborne remotely-sensed data collected as part of this programme of work, we have also located what we believe to be the World’s tallest tropical tree (Shenkin et al., 2019).

(i) From research begun as part of the Carnegie Trust-funded project “Changing species diversity and biomass accumulation in conserved and regenerating tropical forests: two decades on” and subsequently by NERC “Spatio-TEmporal Dynamics of Forest Response to ENSO Drought (STEED)”, we have revisited and re-measured forest plots that were established in the mid-1990s.  In collaboration with researchers from the Universities of Aberdeen and Nottingham, and with support from research assistants of the South East Asian Rainforest Research Programme (SEARRP), data were obtained from 257 plots, representing 51803 individual tree measurements in an area of dipterocarp dominated forest covering nearly 46 hectares.  The majority of plots are located in parts of the forest that has been previously logged some years before and prior research has used satellite remote sensing to estimate the biomass of these forests (Foody et al., 2001; Cutler et al., 2012), showing them to be some of the most productive forests on Earth.

In some parts of the study area forest restoration measures, such as liana cutting and enrichment planting, have taken place in areas managed by the INnoprise FAce PROject INFAPRO project.  A comparison of ACD measured in previous research and compared to measurements in 2015 and 2016 has demonstrated that during the 30 to 35 years after logging, naturally regenerating forest accumulated above-ground carbon at a rate of almost 3 Mg ha-1 yr-1, while those areas with active restoration recovered at a considerably higher rate (Philipson et al. in press).  This research clearly shows the value of applying active restoration to previously logged forests, as well as the ecological and carbon benefits of conserving forests, even those that have been disturbed through activities such as logging.  Our ongoing research is now focusing on the long-term impacts to biodiversity of forest disturbance.

(ii) The El Niño Southern Oscillation is an ocean current phenomena that alters the climate in SE Asia and across the World.  One impact is relatively low precipitation, low cloud cover and higher irradiation over the rainforests of Southeast Asia, but the effects of this short-term climate perturbation on tree physiology and functioning remains poorly understood.  The NERC STEED project examined these impacts by measuring the leaf chemical and structural traits of 104 Malaysian trees in unlogged dipterocarp forests during and after the 2015/16 El Niño.  In collaboration with researchers from the Universities of Aberdeen, Nottingham and Cambridge, and with support from researchers from SEARRP, leaf reflectance was also measured to determine the effectiveness of remote sensing methods for monitoring changes in functional traits. 

The results of this work showed that chlorophyll and carotenoid concentrations were ~35% higher in leaves during the El Niño than afterward, suggesting greening-up of the canopy in response to higher irradiance (Nunes et al., 2019), something that was also noted in satellite imagery collected during this period.  Our findings suggest that plants had a capacity to acclimate rapidly to the loss of the high irradiance conditions during wet periods and to increase pigment synthesis when sunshine hours were high, and that these changes could be monitored using remote sensing.  By demonstrating that changing plant strategies during short-term climate perturbations can be accurately predicted using remote sensing we hope this will be a significant contribution to both understanding tropical forest dynamics and responses to change, as well as the ability to map and monitor these fragile ecosystems across the planet.

Philipson C.D., Cutler M.E.J., Brodrick P.G., Asner G.P., Boyd D.S., Costa P.M., Fiddes J., Foody G.M., van der Heijden G.M.F., Ledo A., Lincoln P.R., Margrove J.A., Milne S., Pinard M.A., Reynolds G., Snoep M., Tangki H., Tay J., Wai Y.S., Wheeler C. and Burslem D.F.R.P.  (in press), Restoration enhances the recovery of aboveground carbon density in logged Bornean tropical forests, Science.

Shenkin, A., Chandler, C., Boyd, D., Disney, M., Majalap, N., Nilus, R., Foody, G., Jami, U., Reynolds, G., Wilkes, P., Cutler, M., van der Heijden, G., Burslem, D., Coomes, D., Bentley, L., Jackson, T., Malhi, Y. (2019), The world’s tallest tropical tree in three dimensions, Frontiers in Forests and Global Change. doi.org/10.3389/ffgc.2019.00032   

Nunes, M.H., Both, S., Philipson, C., Bongalov, B., Brelsford, C., Burslem, D.F.R.P., Coomes, D.A., Majalap, N. & Cutler, M.E.J. (2019) Greening of rainforest leaves, and other trait changes, associated with an El Niño event in Borneo, Env. Res. Letters. doi:10.1088/1748-9326/ab2eae

Cutler, M.E.J., Boyd, D.S. and Foody, G.M. (2012) Estimation of tropical forest biomass with a combination of JERS-1 and Landsat TM data. ISPRS Journal of Photogrammetry and Remote Sensing, 70, 66-77.

Foody, G.M., Cutler, M.E.J., McMorrow, J., Pelz, D., Tangki, H., Boyd, D.S. and Douglas, I., (2001), Mapping the biomass of Bornean tropical forest.  Global Ecology and Biogeography, 10 (4), 379-387.